Example embodiments of the inventive concept relate to a field effect transistor and a method of fabricating the same, and in particular, to a high-voltage field effect transistor and a method of fabricating the same.
A high electron mobility transistor (HEMT), one of compound semiconductor devices, is configured to include one or more layers having very different lattice constants from other layers and thereby its channel layer can have a modified property. Such a lattice mismatch is used to produce a stress improving electron mobility of the channel layer, in the HEMT devices.
There is a difficulty in growing a substrate for the HEMT. For all that, the HEMT can have improved characteristics of power and noise, due to the increase of charge density and high electron mobility in the channel layer, and thus, it can be operated at a higher frequency. Since the HEMT is superior to silicon-based devices in terms of electron mobility, it is widely used for microwave and millimeter-wave applications.
Gallium nitride (GaN), one of nitride semiconductors, is a direct transition semiconductor with a high electron speed of about 2×107 cm/s and a high breakdown electric field of about 3×106 V/cm, and thus, there is an increasing interest in the use of GaN as a new material for high frequency devices. The nitride semiconductors makes it possible to realize as a heterojunction structure, such as AlGaN/GaN, and can be selectively doped, and thus, the use of nitride semiconductor makes it possible to realize a high speed device. In addition, the nitride semiconductor can improve significantly a trade-off relationship between a cutoff frequency (ft) and a breakdown voltage (VBV), which is one of technical issues of conventional field effect transistors. Accordingly, the use of the nitride semiconductor makes it possible to realize electronic devices with high voltage and high frequency property.
By using the nitride-semiconductor-based FET, it is possible to simplify or remove a peripheral circuit, such as a power distribution/synthesis circuit and a direct current (DC) converting circuit, and thereby to realize a high power amplifier module with high power efficiency.
Additionally, to realize better modulating operations and reduced noise characteristics, a T-, Y-, or mushroom-shaped gate electrode having an increased sectional area is used for a high speed semiconductor device. The T-, Y-, or mushroom-shaped gate electrode is generally formed using an E-beam lithography or photolithography process.